Combustion-powered tool having a combined ignition and fuel system

Abstract: For a combustion-powered, fastener-driving tool, a combined ignition and fuel system (10) comprises a battery (12), two normally opened switches namely a head switch (14) and a trigger switch (16), a fuel injector (18) including a solenoid (20) and an associated circuit (22) controlling the fuel injector to enable the fuel injector to inject a combustible fuel for a first time interval, a circuit (24) for producing ignition, and a circuit (26) for monitoring the head and trigger switches (14, 16), for disabling the injector-controlling circuit (22) if the trigger switch (16) is closed while the head switch (14) is open or if both switches are open, for enabling the injector controlling circuit (22) if the trigger switch (16) is closed while the head switch (14) is closed, for enabling the ignition-producing circuit (24) after a second time interval succeeding the first time interval, and for disabling the ignition producing circuit (24) when the injector-controlling circuit (22) is disabled as mentioned. The system further comprises a circuit (60) for monitoring the battery voltage, for comparing the monitored voltage to a reference voltage, and for enabling the injector controlling circuit (22) and the ignition-producing circuit (24) if the monitored voltage is not less than the reference voltage, and for disabling the injector-controlling circuit (22) and the ignition-producing circuit (24) if the monitored voltage is less than the reference voltage.

Description: This invention pertains to a combined ignition and fuel system for a combustion-powered tool, such as a combustion-powered, fastener-driving tool. Combustion-powered, fastener-driving tools, such as combustion-powered, nail-driving tools and combustion-powered, staple-driving tools, are exemplified in Nikolich U.S. Patent Re. 32,452, Nikolich U.S. Patents No. 4,522,162, and No. 4,483,474, Wagdy U.S. Patent No. 4,483,473, and Nikolich U.S. Patent No. 4,403,722 which discloses the features of the preamble of claim 1. Typically, such a tool includes switches that must be closed to enable ignition of a combustible fuel in a combustion chamber by means of a spark plug. These switches include a head switch and a trigger switch. The head switch is closed by pressing a workpiece-contacting element, which is mounted operatively to a nosepiece of the tool, firmly against a workpiece. The trigger switch is closed by pulling a trigger, which is mounted operatively to a handle of the tool. An ignition system for such a tool, employing such head and trigger switches, is disclosed in Rodseth et al. U.S. Patent No. 5,133,329. The ignition system disclosed therein employs photo-electric head and trigger switches, as disclosed in Rodseth U.S. Patent No. 5,191,209. A fuel system for such a tool, employing a fuel injector including a solenoid and an electronic circuit for controlling the solenoid to enable a combustible fuel to flow from a source into the combustion chamber for a time interval after the head switch or the trigger switch is closed, is disclosed in a co-pending patent application filed November 13, 1992, for FUEL SYSTEM FOR COMBUSTION-POWERED, FASTENER-DRIVING TOOL, and assigned commonly herewith. As disclosed in the co-pending application noted above, the time interval is defined by a resistive capacitive network including a thermistor responsive to ambient temperature, along with a resistor arranged to be selectively connected to condition the system for use at higher altitudes and disconnected to condition the system for use at lower altitudes. As disclosed therein, the fuel system can be well integrated with an ignition system according to Rodseth et al. U.S. Patent No. 5,133,329 noted above. In such a tool, as known heretofore, a fan has been employed to produce turbulence in the fuel mixing with air in the combustion chamber. Also, a batterypowered, electric motor has been employed to drive the fan. Since the fan and the electric motor are large contributors to the weight of such a tool and to its manufacturing cost, it would be highly desirable to provide such a tool that could be effectively operated without a fan driven by an electric motor. This invention provides a combustion-powered tool having a combined ignition and fuel system in accordanc with claim 1 of the appended claims. According to a preferred embodiment of this invention for a a combustion-powered tool, a combined ignition and fuel system comprises a battery, two normally opened switches (namely a head switch and a trigger switch) connected to the battery, a fuel injector, means for controlling the fuel injector to enable the fuel injector to inject a combustible fuel for a first time interval, means for producing ignition of the injected fuel, and means for monitoring the head and trigger switches, for disabling the injector controlling means if the trigger switch is closed while the head switch is open or if both switches are open, for enabling the injector controlling means if the trigger switch is closed while the head switch is closed, and for enabling the ignition-producing means after a second time interval commencing after the first time interval has commenced. Preferably, the combined system further comprises battery-monitoring means for monitoring the battery voltage, for comparing the battery voltage monitored thereby to a reference voltage, for disabling the injector-controlling means if the battery voltage monitored thereby is less than the reference voltage, and for enabling the injector-controlling means if the battery voltage monitored thereby is not less than the reference voltage. Preferably, moreover, the battery-monitoring means is arranged for disabling both the injector-controlling means and the ignition-producing means if the battery voltage monitored thereby is less than the reference voltage, and for enabling both the injector-controlling means and the ignition-producing means if the battery voltage monitored thereby is not less than the reference voltage. A preferred embodiment of this invention will now be described with reference to the accompanying drawings, in which:- Figures 1A and 1B are respective halves of a diagram of a combined ignition and fuel system; As shown diagrammatically, a predominantly solidstate, combined ignition and fuel system 10 for a combustion-powered tool, such as a combustion-powered, nail-driving tool or a combustion-powered, stapledriving tool, constitutes a preferred embodiment of this invention. The system 10 comprises a battery 12, a normally opened, photo-electric, head switch 14, a normally opened, photo-electric, trigger switch 16, a fuel injector 18 including a solenoid 20 and arranged to inject a combustible fuel into a combustion chamber (not shown) of the tool, a circuit 22 for controlling the solenoid 20 of the fuel injector 18 so as to control injection of the combustible fuel, a circuit 24 for producing ignition, and a circuit 26 for monitoring the switches 14, 16, in a unique arrangement described below. It is convenient to refer to the circuit 22 as the injector-controlling circuit 22, to refer to the circuit 24 as the ignition-producing circuit 24, and to refer to the circuit 26 as the switch-monitoring circuit 26. Except as illustrated in the drawings and described herein, the fuel injector 18 including the solenoid 20 and the injector-controlling circuit 22 are similar to the fuel system disclosed in Rodseth et al. U.S. Patent No. 5,133,329 noted above, the disclosure of which is incorporated herein by reference. Each of the switches 14, 16, is a photo-electric switch, as disclosed in Rodseth et al. U.S. Patent No. 5,191,209 noted above, the disclosure of which is incorporated herein by reference. Notably, the tool does not employ a fan or an electric, fan-driving motor. Otherwise, except as illustrated and described herein, the combustionpowered tool embodying the system 10 is similar to the combustion-powered, fastener-driving tool illustrated and described in the co-pending application noted above, the disclosure of which is incorporated herein by reference. Thus, as illustrated and described therein, the tool comprises a combustion chamber (not shown) into which a combustible, hydrocarbon fuel is injected by the fuel injector 18 for a time interval (e.g. eight to twelve milliseconds) determined by the injectorcontrolling circuit 20 whereupon injection of the combustible fuel terminates. It is convenient to refer to the time interval discussed in the preceding sentence as a first time interval to distinguish it from a succeeding time interval discussed below. The switch-monitoring circuit 26 is used for monitoring the head switch 14 and the trigger switch 16, for disabling the injector-controlling circuit and the ignition-producing circuit 22 if the trigger switch 16 is closed while the head switch 14 is opened or if both switches are opened, for enabling the injector-controlling circuit 20 if the trigger switch 16 is closed while the head switch 14 is closed, and for enabling the injector-controlling circuit 20 after a second time interval succeeding the first time interval. The battery 12 is a re-chargeable battery comprising a series of nickel-cadmium cells, having a rated voltage of 6.25 volts, and having a rated current of 1.5 amp-hours. The head switch 14 comprises a photo-transmissive diode 14a, a photo-receptive transistor 14b, and a shutter 14c and is regarded as opened when the photo-receptive transistor 14b is non-conductive and as closed when the photo-receptive transistor 14b is conductive. The trigger switch 16 comprises a photo-transmissive diode 16a, a photo-receptive transistor 16b, and a shutter 16c and is regarded as opened when the photo-receptive transistor 16b is non-conductive and as closed when the photo-receptive transistor 16b is conductive. Essentially, each of these switches 14, 16, is similar to the photo-electric switch disclosed in the co-pending application noted above. The head switch 14 is closed by pressing a workpiece-contacting element, which is mounted operatively to a nosepiece of the tool, firmly against an workpiece. The trigger switch 16 is closed by pulling a trigger, which is mounted operatively to the handle, with the index finger of the same hand. The workpiece-contacting element, the nose-piece, and the handle are not shown. When each of these switches 14, 16, is closed, the shutter of the switch is moved from a normal position, in which the shutter prevents light from the photo-transmissive diode thereof from reaching the photo-receptive transistor thereof, into a displaced position, in which the shutter permits light from the photo-transmissive diode to reach the photo-receptive transistor. The shutter is biased toward the normal position. Thus, if there is a failure, such as a severed wire, a failed diode, or a failed transistor, such switch does not become falsely closed. Generally, the ignition-producing circuit 18 comprises a spark plug 30 having a spark gap 32, a capacitor 36 (1.0 µf) for producing a spark across the spark gap 32 upon a sudden discharge of the capacitor 36, a circuit 38 comprising a charge-pump oscillator 40 for charging the capacitor 36, and a circuit 42 including a silicon-controlled rectifier 44 for producing a sudden discharge of the capacitor 36. The switch-monitoring circuit 26 is arranged to enable the capacitor-charging circuit 38 if the trigger switch 16 is closed while the head switch 14 is closed and to disable the capacitor charging circuit 38 if the trigger switch 16 is closed while the head switch 14 is opened or if the head switch 14 and the trigger switch 16 are both opened. Normally, therefore, the switch monitoring circuit 26 disables the capacitor-charging circuit 38. Moreover, the ignition system 10 comprises a battery-monitoring circuit 60 for monitoring the battery 12 and for comparing the battery voltage monitored to a reference voltage for the battery 12. The battery-monitoring circuit 60 is arranged to enable the capacitor-charging circuit 38 if the battery voltage monitored by such circuit 60 is not less than the reference voltage for the battery 12. Also, the battery-monitoring circuit 60 is arranged to disable the capacitor-charging circuit 38 if the battery voltage monitored by such circuit 60 is less than the reference voltage for the battery 12, whereby ignition cannot occur. Furthermore, the ignition system 10 comprises a capacitor-monitoring circuit 70 for monitoring a capacitor voltage, namely the voltage to which the capacitor 36 is charged by the capacitor-charging circuit 38, and for comparing the capacitor voltage monitored by such circuit 70 to a reference voltage for the capacitor 36. The capacitor-monitoring circuit 70 is arranged to enable the circuit 42 including the silicon-controlled rectifier 44 for producing a sudden discharge of the capacitor 36 if the capacitor voltage monitored by the circuit 70 is not less than the reference voltage for the capacitor 36 and for disabling the same circuit if the capacitor voltage monitored by the circuit 70 is less than the reference voltage for the capacitor 36. The switch-monitoring circuit 26 does not monitor the head switch 14 and the trigger switch 16 continuously. Rather the switch-monitoring circuit 26 is arranged for polling the head switch 14 intermittently to determine whether the head switch 14 is closed and for polling the trigger switch 16 intermittently to determine whether the trigger switch 16 is closed, whereby battery energy is conserved. In the switch-monitoring circuit 26, as shown in Figure 1, the photo-transmissive diodes 14a, 16a, of the respective switches 14, 16, are connected in series between the positive terminal of the battery 12 and ground, via the switch-monitoring circuit 26, so as to be intermittently connected to the positive terminal of the battery 12 as such circuit 20 polls the respective switches 14, 16. The photo-receptive transistor 14b of the head switch 14 is connected to the positive terminal of the battery 12, through a resistor 78 (10 K Ω ), and to the input pin of an inverter (Schmitt trigger) 80, through a resistor 82 (100 K Ω). When the head switch 14 is closed, i.e. when the photo-receptive transistor 14b becomes conductive, the input voltage to the inverter 80 drops low and the output voltage from the inverter 80 goes high. The photo-receptive transistor 16b of the trigger switch 16 is connected to the positive terminal of the battery 12, through a resistor 84 (10 K Ω), and to the input pin of an inverter (Schmitt trigger) 86, through a resistor 88 (100 K Ω). When the trigger switch 16 is closed, i.e. when the photo-receptive transistor 16b becomes conductive, the input voltage to the inverter 86 drops to a low voltage whereupon the output voltage from the inverter 86 rises to a high voltage. If the output voltage from the inverter 80 is high, the capacitor-charging circuit 38 is enabled. If the output voltage from the inverter 80 is low, the capacitor-charging circuit 38 is disabled. So long as the head switch 14 and the trigger switch 16 are both opened, which means that the photo-receptive transistors 14b, 16b, are non-conductive, the input voltages to the respective inverters 80, 86, are high and the output voltages from the respective inverters 80, 86, are low. A transistor 90 is connected between the output pin of the inverter 86 and the input pin of the inverter 80, through a diode 92, which is forward biased when the transistor 90 is switched on. The base of the transistor 90 is connected to the output pin of the inverter 80, through a resistor 94 (100 K Ω). A capacitor 96 (0.001 µf) is connected between the input pin of the inverter 80 and the negative terminal of the battery 12. If the trigger switch 16 is closed while the head switch 14 is opened, i.e. if the photo-receptive transistor 16b becomes conductive while the photo-receptive transistor 14b is non-conductive, the transistor 90 is switched on to apply a high voltage to the input pin of the inverter 80. Also, if signals indicating that the head switch 14 and the trigger switch 16 are closed are received simultaneously, the delay caused by the capacitor 96 ensures that the transistor 90 is switched on and that the transistor 90 applies a high voltage to the input pin of the inverter 80. As a result, the input to the inverter 80 is latched high, and the output from the inverter 80 is low. If the trigger switch 16 is closed while the head switch 14 is closed, i.e. if the photo-receptive transistors 14b, 16b, become conductive, the transistor 90 is switched off so that no high voltage is applied to the input pin of the inverter 80. A transistor 116 is connected between the positive terminal of the battery 12 and the series-connected, photo-transmissive diodes 14a, 16a, of the respective switches 14, 16, via a resistor 118 (1 Ω, 1/8 W), to connect such diodes 14a, 16a, to the positive terminal of the battery 12 whenever the transistor 116 is switched on. An oscillator 120, which has a conventional configuration, comprises an inverter (Schmitt trigger) 122 and a resistor 124 (2 M Ω) in parallel, a resistor 126 (12 K Ω) and a diode 128 in parallel therewith, and a capacitor 130 (0.22 µf) connecting the input pin of the inverter 122 to the negative terminal of the battery 12. The output pin of the inverter 122 is connected to the base of the transistor 116 via a resistor 132 (3.3 K Ω), so as to switch the transistor 116 on and off intermittently as the oscillator 120 oscillates, thereby to conserve battery energy as the respective switches 14, 16, are polled. The input pin of the inverter 122 is connected to the output pin of the inverter 100 via a diode 134. When the output voltage from the inverter 100 is a low voltage, the oscillator 120 is latched via the diode 134 so that the output voltage from the inverter 122 remains high. The transistor 116 is connected via a resistor 136 (100 Ω) and a diode 138 to a green light-emitting diode 140, which flashes intermittently as the transistor 116 is switched on and off intermittently, as an indicator that the ignition system 10 is in a stand-by mode. Also, the green light-emitting diode 140 is lighted steadily when the oscillator 120 is latched so that the output voltage from the inverter 122 remains high, as an indicator that the ignition system 10 is in a ready mode or in a delay mode. A transistor 148 and a red light-emitting diode 150 are connected in parallel with the diode 138 and the green light-emitting diode 140. The battery-monitoring circuit 60 comprises a comparator (operational amplifier) 160 having a reference pin, an input pin, and an output pin. A resistor 162 (100 K Ω) is connected between the reference pin of the comparator 160 and the positive terminal of the battery 12. A voltage reference diode 164 is connected between the reference pin of the comparator 160 and the negative terminal of the battery 12. Via the resistor 162 and the voltage reference diode 164, a reference voltage for the battery 12 is applied to the reference pin of the comparator 160. A voltage divider 166 comprising a resistor 168 (301 K Ω, 1%) connected between the positive terminal of the battery 12 and the input pin of the comparator 160, a resistor 170 (100 K Ω, 1%) connected to the negative terminal of the battery 12, and a resistor 174 (10 M Ω) connected between the input and output pins of the comparator 160 applies a voltage proportional to the battery voltage to the input pin of the comparator 160. If the voltage applied to the input pin of the comparator 160 is not less than the reference voltage for the battery 12, the voltage at the output pin of the comparator 160 is high. If the voltage applied thereto is less than the reference voltage for the battery 12, the voltage at the output pin of the comparator 160 is low. The voltage at the output pin of the comparator 160 is applied via a resistor 176 (3.3 K Ω) to the base of the transistor 148. If the voltage applied to the base of the transistor 148 is low, the transistor 148 is switched on, so as to create a short circuit across the diode 138 and the green light-emitting diode 140, and so as to light the red light-emitting diode 150 steadily, as an indicator that the battery voltage is inadequate. If the output voltage applied thereto is a high voltage, the transistor 148 is not switched on, and the green light-emitting diode 140 can be then lighted. The capacitor-charging circuit 38 is connected to the positive terminal of the battery 12 via a resistor 188 (100 K Ω) and a latching circuit 190. The latching circuit 190 comprises an inverter (Schmitt trigger) 192 having its input pin connected to the resistor 188, a transistor 194 connected to the input pin of the inverter 192, a resistor 196 (100 K Ω) connected between the output pin of the inverter 192 and the base of the transistor 194, and a capacitor 198 (0.01 µf) connecting the input pin of the inverter 192 to the negative terminal of the battery 12. The transistor 194 is connected to the output pin of the comparator 160. Normally, the output voltage from the inverter 192 is a high voltage, which switches on the transistor 194. When the output voltage from the comparator 160 is a low voltage, which means that the battery voltage is insufficient, the transistor 194 remains switched on to disable the capacitor-charging circuit 38. As long as the output voltage from the comparator 160 is a low voltage, the latching circuit 190 is latched on and continues to disable the capacitor-charging circuit 38 until the output of the comparator 160 is a high voltage, which means that the battery voltage is sufficient for proper operation. The resistor 188, the capacitor 198, and the input pin of the inverter 192 are connected to the output pin of the inverter 80, via a diode 202. When the output voltage from the inverter 80 is low, the voltage applied to the input pin of the inverter 192 is insufficient to cause the inverter 192 to invert. Also, when the transistor 194 is conducting, the voltage applied to the input pin of the inverter 192 is insufficient to cause the inverter 192 to invert. Otherwise, when the output voltage from the inverter 80 is high, a high voltage is applied to the input pin of the inverter 192. Thus, the inverter 192 exhibits a low voltage from its output pin. Via the resistor 196, the low voltage from the output pin of the inverter 192 is applied to the base of the transistor 194, which is switched off, which means that the latching circuit 190 is off. At this time, even if the battery voltage drops transiently below the reference voltage for the battery 12 when the capacitor-charging circuit 38 is operating, the latching circuit 190 does not disable the capacitor-charging circuit 38. Via a diode 286, the output pin of the inverter 192 is connected to the charge-pump oscillator 40 of the capacitor-charging circuit 38. The charge-pump oscillator 40, which has a conventional configuration, comprises an inverter (Schmitt trigger) 222 and a resistor 226 (820 K Ω) in parallel, a resistor 224 (130 K Ω) and a diode 228 in parallel therewith, and a capacitor 230 (0.001 µf) connecting the input pin of the inverter 222 to the negative terminal of the battery 12. The output voltage from the output pin of the inverter 222 is connected via a resistor 232 (3.3 K Ω) to the base of a Darlington transistor 234, which is connected in series with the primary winding of a step-up transformer 240. The primary winding of the transformer 240 is connected to the positive terminal of the battery 12. The secondary winding of the transformer 240 is connected via a diode 242 to the capacitor 36. Thus, as the charge-pump oscillator oscillates, the capacitor 36 is charged stepwise. The capacitor 36 is connected in series with the primary winding of an output transformer 250. A diode 252 connected in parallel with the capacitor 36 and the primary winding of the transformer 250 is intended to be normally non-conductive but to break down so as to increase the spark duration in a manner explained below. The secondary winding of the transformer 250 is connected to one electrode of the spark plug 30. The other electrode of the spark plug 30 is grounded. Thus, upon a sudden discharge of the capacitor 36, a spark is produced at the spark gap 32 of the spark plug 30. The silicon-controlled rectifier 44 is connected in parallel with the capacitor 36 and the primary winding of the transformer 250, and in parallel with the diode 252, so as to produce a sudden discharge of the capacitor 36 through the primary winding of the transformer 250 when the silicon-controlled rectifier 44 is switched on. After the initial, sudden discharge, reverse induced current is allowed to flow through the primary of the transformer 250 via the diode 252, which recharges the capacitor 36. This charge/discharge/re-charge oscillation between the primary of the transformer 250 and the capacitor 36 greatly increases the spark duration time. In the capacitor-monitoring circuit 70, a voltage divider 254 comprising a resistor 256 (10 M Ω) connected to the capacitor 36, a resistor 258 (46.4 K Ω, 1%) and a capacitor 260 (0.022 µf) connected in parallel between the resistor 256 and the negative terminal of the battery 12, and a resistor 262 (10 K Ω) applies a voltage proportional to the voltage to which the capacitor 36 has been charged to the input pin of a comparator (operational amplifier) 270. The resistor 162 noted above in a context of the comparator 160 is connected between the reference pin of the comparator 270 and the positive terminal of the battery 12. The voltage reference diode 164 noted above in the same context is connected between the reference pin of the comparator 270 and the negative terminal of the battery 12. Via the resistor 162 and the voltage reference diode 164, a reference voltage for the capacitor 36 is applied to the reference pin of the comparator 270. Because the resistor 162 and the voltage reference diode 164 define the reference voltage for the capacitor 36 as well as the reference voltage for the battery 12, the reference voltages therefor are equal. If the voltage applied to the input pin of the comparator 270 is not less than the reference voltage for the capacitor 36, the output voltage from the output pin of the comparator 270 is high. If the voltage applied to the input pin of the comparator 270 is less than the reference voltage for the capacitor 36, the output voltage from the output pin of the comparator 270 is low. A high voltage from the output pin of the comparator 270 is applied, via a diode 282, to the input pin of the inverter 222 so as to latch the output of the inverter 222 low. A new ignition cannot be then initiated until the trigger switch 16 has been opened. So as to stabilize the circuits and to minimize susceptibility to false triggering stimuli from outside sources, such as radio frequency interference and electrical noise, a capacitor 290 (10 µf) is connected across the battery 12. Moreover, a capacitor 292 (0.047 µf) is associated with the resistor 82, so as to protect the inverter 80, and a capacitor 294 (0.047 µf) is associated with the resistor 88, so as to protect the inverter 86. The green light-emitting diode 140 and the red light-emitting diode 150 function as mode indicators. When the green light-emitting diode 140 is flashing, the ignition system 10 is in a low current consumption, standby mode, in which the battery voltage monitored by the battery-monitoring circuit 60 is not less than the reference voltage for the battery 12 and in which the head switch 14 and the trigger switch 16 are both opened. When the green light-emitting diode 140 is lighted steadily, the ignition system 10 is in a ready mode, in which the head switch 14 has been closed or the trigger switch 16 has been closed, or in a delay mode, in which the head switch 14 and the trigger switch 16 have been opened. After a time delay, the ignition system 10 leaves the delay mode and reenters the standby mode. Also, the ignition system 10 has an ignition mode, which it enters from the ready mode when the trigger switch 16 is closed and which it leaves when the trigger switch 16 is opened. Except as illustrated and described herein, the fuel injector 18 is similar to the fuel injector disclosed in the co-pending application noted above. Thus, the fuel injector 18 includes the solenoid 20, which has a solenoid coil 302, and the injector controlling circuit 22, which is similar in many respects to the injector-controlling circuit disclosed in such co-pending application. The injector-controlling circuit 22 includes a solenoid driver 320 of a known type, namely a Model MC3484S2-1 integrated, monolithic solenoid driver available commercially from Motorola, Inc. of Schaumburg, Illinois. Details of the solenoid driver 320 and its operation are well known to persons having ordinary skill in the art and are outside the scope of this invention. Pin 1 of the solenoid driver 320 is connected in a manner to be later described. Pin 2 thereof is connected to the negative terminal of the battery 12, via a resistor 322 (1 K Ω) and to pin 5 thereof, via a resistor 324 (18 K Ω). Pin 3 thereof is connected to the negative terminal of the battery 12. Pin 4 thereof is connected to a selected end of the solenoid coil 302. Pin 5 thereof is connected to pin 2 thereof, via the resistor 324, to the positive terminal of the battery 12, and to the opposite end of the solenoid coil 302. A zener diode 326 is connected between the selected end of the solenoid coil 302 and the negative terminal of the battery 12 so as to protect the solenoid driver 320 against high counter voltages when electromagnetic fields in the solenoid coil 302 collapse. The respective ends of the solenoid coil 302 to be thus connected to pins 4 and 5 of the solenoid driver 320 are selected so that a valve (not shown) of the fuel injector 18 is opened by the solenoid coil 302 when the solenoid coil 302 is energized and closed by a spring (not shown) of the solenoid 300 when the solenoid coil 302 is de-energized. The solenoid driver 320 is arranged so that, when a high voltage is applied to pin 1 thereof, the solenoid coil 302 is energized, and so that, when the high voltage applied thereto is removed, the solenoid coil 302 is de-energized. Also, the circuit 20 comprises a resistor 332 (100 K Ω) and an inverter (Schmitt trigger) 338 having its input pin connected to the positive terminal of the battery 12, via the resistor 332. A resistor 340 (510 K Ω) is connected to the output pin of the inverter 338. A thermistor 342 (500 K Ω) is connected in parallel with the resistor 340. A resistor 344 (1 M Ω) and a switch 346 are arranged so that the resistor 344 can be selectively connected in parallel with the resistor 340 and with the thermistor 342 by closing the switch 346 and disconnected by opening the switch 346. A variable resistor 348 (1 M Ω) is connected to the resistor 340, to the thermistor 342, and to the resistor 344 if the switch 346 is closed. A capacitor 350 (0.01 µf) is connected between the variable resistor 348 and the negative terminal of the battery 12. The variable resistor 348 and the capacitor 350 are connected to the input pin of an inverter (Schmitt trigger) 352. The output pin of the inverter 352 is connected, via a diode 354, to the input pin of an inverter (Schmitt trigger) 356. The diode 354 is arranged to block reverse current through the inverter 352. The output pin of the inverter 338 is connected, via a resistor 358 (22 K Ω), to the input pin of the inverter 356. A capacitor 360 (0.001 µf) is connected between the input pin of the inverter 356 and the negative terminal of the battery 12. The output pin of the inverter 356 is connected to pin 1 of the solenoid driver 330. The several inverters (Schmitt triggers) noted above are provided by a Model 74HC14M (CMOS) device available commercially from National Semiconductor Corporation of Santa Clara, California. The resistor 340, the thermistor 342, the resistor 344 if connected, and the capacitor 350 define a resistive-capacitive network for defining a first time interval, during which the solenoid coil is energized to open the valve of the fuel injector 60. The thermistor 342 is a resistor having a negative temperature co-efficient of resistance. Thus, the first time interval is shorter at higher temperatures, at which less fuel is required. Also, the first time interval is longer at lower temperatures, at which more fuel is required. The first time interval is shorter when the resistor 344 is connected in parallel with the resistor 340 and with the thermistor 342 and longer when the resistor 344 is disconnected. When the resistor 344 is connected in parallel therewith, the tool is conditioned for use at higher altitudes, at which less fuel is required. When the resistor 344 is disconnected, the tool is conditioned for use at lower altitudes, at which more fuel is required. A variable resistor (not shown) for conditioning the tool for use over a range of altitudes can be advantageously substituted for the resistor 344. The variable resistor 348 can be suitably varied to condition the tool for use with different fuels. The resistor 358 and the capacitor 360 define a resistive-capacitive network for effecting a time delay between switching of the output of the inverter 338 from high to low and energisation of the solenoid coil 302. When the voltage at the input pin of the inverter 338 is low, high voltage is applied by the output pin of the inverter 338 to the input pin of the inverter 352, via the parallel resistors including the resistor 340 and the thermistor 342 and via the variable resistor 348, whereby the capacitor 350 is charged. High voltage is applied by the output pin of the inverter 338 to the input pin of the inverter 356, via the resistor 358, whereby the capacitor 360 is charged. Although low voltage is present at the output pin of the inverter 352, the diode 354 does not permit the capacitor 360 to discharge to the output pin of the inverter 352. When the voltage at the input pin of the inverter 338 is switched from low to high, the voltage at the output pin of the inverter 338 drops sufficiently for the inverter 338 to switch its state, whereupon the capacitor 350 begins to discharge, via the resistor 348 and via the resistor 340, the thermistor 342, and the resistor 344 if connected, to the output pin of the inverter 338 and the capacitor 360 begins to discharge, via the resistor 358, to the output pin of the inverter 338. The capacitor 360 discharges more rapidly. As the capacitor 360 discharges, the voltage at the input pin of the inverter 356 drops. When the capacitor 360 has discharged sufficiently for the inverter 356 to switch its state, high voltage is applied by the output pin of the inverter 356 to pin 1 of the solenoid controller 320, whereupon the solenoid coil 302 is energized. Thus, there is a time delay between switching of the output voltage of the inverter 338 from low to high and energisation of the solenoid coil 302. The voltage at the output pin of the inverter 352 remains low until the capacitor 350 has discharged sufficiently for the inverter 352 to switch its state. The resistor 358 and the capacitor 360 also provide some protection against transient voltages. When the capacitor 350 has discharged sufficiently for the inverter 352 to switch its state, high voltage is applied to the input pin of the inverter 356. Because the diode 354 provides minimal impedance compared to the resistor 358, the inverter 356 switches its state, even if the voltage at the output pin of the inverter 338 remains low. Thus, the voltage applied by the output pin of the inverter to pin 1 of the solenoid controller drops, whereupon the solenoid coil is de-energized. The input pin of the inverter 338 is connected to the output pin of the inverter 86 and to the transistor 90, via a diode 368. Thus, whenever the output voltage from the inverter 86 is low or the transistor 90 is conducting, the diode 368 is conducting so that the input voltage to the inverter 338 remains low. The input pin of the inverter 338 is connected to the output pin of an inverter (Schmitt trigger) 370, via a diode 372. The input pin of the inverter 370 is connected to the output pin of the inverter 192. Thus, whenever the output voltage from the inverter 192 is high so that the output voltage from the inverter 370 is low, the diode 372 is conducting so that the input voltage to the inverter 338 remains low. Therefore, the output voltage from the inverter 338 does not switch from high to low unless the trigger switch 16 is closed while the head switch 14 is closed, whereby the output voltage from the inverter 86 is switched from low to high and the transistor 90 is switched off, and unless the battery voltage is sufficient, whereby the output voltage from the inverter 192 is switched from high to low so that the output voltage from the inverter 370 is switched from low to high. As explained below, the injector-controlling circuit 22 is inter-connected with the switch-monitoring circuit 26 and with the ignition-producing circuit 24, so as to produce ignition after a second time interval (e.g. five to eight milliseconds) succeeding the first time interval. The output pin 352 of the inverter 352 is connected to the input pin of an inverter (Schmitt trigger) 380, via a resistor 382 (820 K Ω), and a capacitor 384 (0.01 µf) is connected to the input pin of the inverter 380. The resistor 382 and the capacitor 384 define a resistive-capacitive network for determining the second time interval. When the voltage output from the inverter 352 switches from low to high, the capacitor 384 begins to charge. After the second time interval, when the capacitor 384 has become sufficiently charged, the output voltage from the inverter 380 is switched from high to low. The output pin of the inverter 380 is connected to the input pin of an inverter 390. The output pin of the inverter 390 is connected via a voltage divider 382, which comprises a resistor 394 (3.3 K Ω) and a resistor 396 (1 K Ω) connected between the resistor 394 and the negative terminal of the battery 12, to the gate of the silicon-controlled rectifier 44. When the output voltage from the inverter 380 is switched from high to low, the output voltage from the inverter 390 is switched from low to high. When the output voltage from the inverter 390 is switched from low to high, a high voltage is applied to the gate of the silicon-controlled rectifier 44, which is switched on so as to produce a sudden discharge of the capacitor 36 through the primary winding of the output transformer 250. The sudden discharge of the capacitor 36 produces ignition at the spark plug 30. The output pin of the inverter 390 is connected to the resistor 262, where the resistor 262 is connected to the resistor 258 and the capacitor 260, via a diode 398. When a high voltage is applied to the gate of the silicon-controlled rectifier 44, a high voltage is applied to the input pin of the comparator 270, and the capacitor 260 is charged. Thus, when the silicon-controlled rectifier 44 is switched on, the output of the comparator 270 is latched high so as to disable the capacitor-charging circuit 42 while ignition is being produced. Because the second time interval is short (e.g. five to eight milliseconds) ignition is produced while the injected fuel continues to swirl turbulently in the combustion chamber. It is not necessary, therefore, to employ a fan to produce turbulence in the combustion chamber. The several inverters (Schmitt triggers) noted above are provided by Model 74HC14M (CMOS) devices available commercially from National Semiconductor Corporation of Santa Clara, California. Herein, all values stated parenthetically for elements of the system 10 are exemplary values, which are useful in a preferred example of the preferred embodiment illustrated in the drawings and described above. Such values are not intended to limit this invention.

Claims: A combustion-powered tool having a combined ignition and fuel system (10), comprising a fuel injector (18), injection control means (22) for controlling the fuel injector to inject a combustible fuel, and ignition control means (24) for producing ignition of the combustible fuel characterised in that the injection control means (22) injects fuel for a first predetermined time interval, and the ignition controlling means (24) ignites fuel after a second predetermined time interval commencing after the first predetermined time interval has commenced. A system according to claim 1, wherein the injector control means (22) is arranged to enable the ignition control means (24) when the first predetermined time interval has elapsed. A system according to claim 1 or 2, wherein the first time interval is about eight to about twelve milliseconds and the second predetermined time interval is about five to about eight milliseconds. A combustion-powered tool according to any one of the preceeding claims, comprising a battery (12), a normally opened head switch (14) and a normally opened trigger switch (16), both being connected to the battery (12), means (26) for monitoring the head (14) and trigger (16) switches, for disabling the injector control means (22) if the trigger switch (16) is closed while the head switch (14) is open or if both switches are open, and for enabling the injector control means (22) if the trigger switch (16) is closed while the head switch (14) is closed. A combustion powered tool according to claim 4, wherein the means (26) for monitoring the head (14) and trigger (16) switches is arranged for disabling the ignition control means (24) when the injector control means (22) is disabled. A combustion powered tool according to claim 4 or 5, further comprising means (60) for monitoring the battery voltage, for comparing the battery voltage monitored thereby to a reference voltage, for disabling the injector control means (22) if the battery voltage monitored thereby is less than the reference voltage, and for enabling the injector control means (22) if the battery voltage monitored thereby is not less than the reference voltage. A combustion powered tool according to claim 6, in which said means (60) for monitoring the battery voltage also disables the ignition control means (24) if the battery voltage monitored thereby is less than the reference voltage, and enables the ignition control means (24) if the battery voltage monitored thereby is not less than the reference voltage. A combustion powered tool according to any one of claims 4 to 7, wherein the means (26) for monitoring the head (14) and trigger (16) switches is arranged for disabling the ignition control means (24) when the injector control means (22) is disabled.

Inventors: DOHERTY JAMES E, VEOUKAS STANLEY C, WENDLING ERNEST J, DOHERTY, JAMES E., VEOUKAS, STANLEY C., WENDLING, ERNEST J.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1994
Main classification: B25C1
IPC codes: F02P9, F02P15, F02P3, F02P11, F16K31, B25C1, F02D41